This application is a continuation-in-part of application Ser. No. 350,521 filed May 11, 1989, entitled Reverse Osmosis System And Automatic Cycling Booster Pump Therefor, now U.S. Pat. No. 5,000,845 which in turn is a continuation-in-part of application Ser. No. 111,697 filed 21, 1987, entitled Reverse Osmosis System And Automatic Cycling Booster Pump Therefor, now U.S. Pat. No. 4,836,924 issued Jun. 6, 1989.
Reverse osmosis systems are commonly used for removing impurities from water, such as drinking water. A conventional reverse osmosis system includes a reverse osmosis filter having a reverse osmosis membrane. Feed water is supplied to the filter, and the filter delivers filtered product water having a reduced impurity content. Not all of the feed water supplied to the filter passes through the reverse osmosis membrane, and this unfiltered water, or brine, can be discharged to drain or a portion of it can be recycled through the filter.
To increase the throughput, i.e., the volume of product water, it is known to employ a pump to increase the pressure of the feed water supplied to the reverse osmosis filter. A conventional electric motor driven pump is used for this purpose. Motor driven pumps increase installation costs by requiring electrical wiring to the pump. In addition, they are subject to higher operational costs due to the cost of electricity and the cost of maintaining and repairing or replacing the electrical motor.
My U.S. Pat. No. 4,836,924 and my copending Ser. No. 350,521 disclose pumps or pressure intensifiers which are driven by the feedwater to increase the pressure of the feedwater supplied to the reverse osmosis filter. Each of these pressure intensifiers employs a pumping member driven on a pumping stroke by the feedwater under pressure to increase the pressure of the feedwater so that the reverse osmosis filter receives feedwater at increased pressure. The pumping member is also movable on a return stroke without increasing the pressure of the feedwater. When using a pump or pressure intensifier of this type, the reverse osmosis filter is supplied with feedwater at increased pressure during the pumping stroke but not during the return stroke.
In order to continuously supply feedwater at boosted pressure to the reverse osmosis filter, it is known to employ two pressure intensifiers driven out of phase, with each of the pressure intensifiers supplying boosted pressure feedwater to the reverse osmosis filter during a pumping stroke. Systems of this type are shown, for example, in Wilson U.S. Pat. No. 4,367,140 and published U.K. patent application No. GB 2,088,968 A.
In order to utilize two pressure intensifiers in this manner, it is necessary to appropriately sequence the pumping and return strokes of the two pressure intensifiers. The systems disclosed in the Wilson patent and the British application employ relatively complex techniques for sequencing the pressure intensifiers.